Nasal cannulas are well-known devices for delivering low flows (1-6 l/min.) of supplemental or therapeutic oxygen to persons needing additional oxygen, where detailed control of respiration rate is not required. Such devices find significant use in elderly patients who need oxygen therapy. Typically, nasal cannulas include a hollow body portion having a pair of spaced-apart, curved elongated tubular portions (nasal interface or nasal prongs) extending through a surface of the body and in fluid communication with the hollow volume thereof. The tubular portions through which oxygen is caused to flow are adapted to fit into the nares of a person. Two flexible plastic tubes in fluid contact with a source of oxygen are attached to the body, one at each end thereof, are disposed behind the ears of a person and brought into mechanical contact under the chin of the person by means of a loop adjustment collar or slide, as an example. Cannulas may be single lumen in which situation a single flow path exists between the patient and a source of oxygen, that is, the plastic tubes may merge into a single tube by means of a tee under the chin, as an example, or dual lumen where the flow paths to each naris may be separated by a barrier or bifurcation, and the two plastic tubes are supplied using different oxygen sources or gas regulators, as examples.
Oro-nasal cannulas are also known, although uncommon, wherein a third plastic tube is run parallel to one of the nasal supply tubes and mechanically coupled thereto. The third tube may be connected to a second or third oxygen source or gas regulator, depending upon the design of the nasal portion of the cannula. Through insertion of the tubular extensions into the nares, looping the oxygen supply tubes over the ears and combining the tubes under the chin, as an example, a nasal or oral-nasal cannula may be firmly affixed to a person, wherein it remains in place during periods of sleep or walking, as examples.
Patients undergoing continuous oximetry monitoring (measurement of oxygen saturation of the blood by means of an oximeter) often display desaturation while sleeping. Plethysmographic assessment of the individual generally uncovers no change in the air volume flowing, and the patient must be awakened and encouraged to breathe through the nose, wherein oxygen saturation improves. As the patient returns to sleep, the cannula remains in the nose, and desaturation returns. Thus, nasal cannulas positioned in the nares are ineffective for delivery of oxygen to mouth breathers. Further, breathing impairment conditions such as nasal/sinus congestion, nose bleeds, deviated septum, and nose injury, all prevent proper oxygen saturation using a nasal cannula positioned in the nares. An Oximizer® oxygen-conserving nasal cannula may be useful for better oxygen delivery at higher oxygen flow levels, but the difficulty remains for mouth breathing individuals and those with breathing impairments.
Oral oxygen delivery using masks (simple masks, face tents, and non-rebreather, venturi and BiPAP (Bi-level Positive Airway Pressure) masks, as examples) are an option. However, CO2 retention, claustrophobia, drying of mucus membranes, communication difficulties, expense and considerable oxygen use make such options less attractive. High oxygen use is generally a problem with oro-nasal cannulas since the oxygen flow may ineffectively continue through the nasal portion of the cannula.